Susie and Kris are classmates. They both come to class late, and as a result, Alphys makes the two partners for the group project. As they notice the chalk is missing, Alphys sends Kris and Susie to go look for more chalk. Susie leaves the classroom first. As Kris follows, they spot Susie eating chalk. Susie notices Kris and threatens them.
Susie and Kris proceed to get into an abandoned classroom to get chalk. As they get in, they are unable to find a light switch and the door shuts behind them. They soon fall through the floor and end up in the Dark Realm.
Kris and Susie are separated at first, but meet up after Kris frees her. The two meet Ralsei, who tells them that they are part of a prophecy. Susie doesn't believe it and leaves Kris with Ralsei. Later, Kris and Ralsei find Susie. She joins their team but attacks foes instead of doing what Kris tells her to do.
As Susie becomes frustrated with Ralsei's demands not to attack enemies, she joins Lancer, making Kris and Susie temporary enemies. She joins the party again after Kris and Ralsei defeat her in a battle.
Kris, Susie and Ralsei are later imprisoned by Lancer, as he doesn't want them and his father to attack each other. Susie manages to escape and free the other two, reuniting the team. This time, Susie agrees to do what Kris says instead of only fighting.
After the battle against the King, Kris and Susie return to their school, now on better terms than before. The two leave the school building as school has already ended.
When exploring the town, Kris can talk to Noelle and tell her about Susie.
Krusie is a somewhat popular Deltarune ship, Occasionally getting into conflict with Suselle. Some prefer Krusie over Suselle as Kris and Susie have more known interactions. On AO3, it is the second most popular romantic ship for both characters and the fourth most popular romantic ship in the Deltarune fandom. Their friendship is the third most popular overall ship with the Deltarune fandom tag.